Method and apparatus for dynamically selecting a frequency reuse plan for a radio messaging system

ABSTRACT

A method and apparatus in a radio messaging system monitors (304, 404), by a plurality of base receivers (207), an inbound channel for an inbound transmission from a portable subscriber unit (122), and determines (306, 406) a subset of the plurality of base receivers that reliably receive the inbound transmission. The method and apparatus then selects (310, 408) a frequency reuse plan for the radio messaging system, based upon the subset.

FIELD OF THE INVENTION

This invention relates in general to radio communication systems, andmore specifically to a method and apparatus in a two-way radio messagingsystem for dynamically selecting a frequency reuse plan for an outboundtransmission from a fixed portion of the radio messaging system to aportable subscriber unit.

BACKGROUND OF THE INVENTION

Modern two-way messaging systems employ frequency reuse for spectrallyefficient communication with portable subscriber units. Correctestimation of how many and which subscriber units can simultaneouslyreceive different messages from different base transmitters withoutundue interference is difficult. A prior art technique has been for thesubscriber unit to measure the quality of a received color codecorresponding to a base transmitter. Another prior art technique hasbeen to estimate the location of the subscriber unit from receivedsignal strength at the base receivers.

These prior art techniques have not always provided a reliable estimateof the optimum frequency reuse plan for communication with thesubscriber unit. Quality of color code reception and subscriber unitlocation cannot always determine how many and which base transmittersare within range of the subscriber unit.

Thus, what is needed is a method and apparatus that can dynamicallyselect a frequency reuse plan for communicating with a portablesubscriber unit. Preferably, the selected frequency reuse plan should beclosely related to how many and/or which transmitters are within rangeof the subscriber unit.

SUMMARY OF THE INVENTION

An aspect of the present invention is a method in a two-way radiomessaging system for dynamically selecting a frequency reuse plan. Themethod comprises the steps of monitoring, by a plurality of basereceivers, an inbound channel for an inbound transmission from aportable subscriber unit, and determining a subset of the plurality ofbase receivers that reliably receive the inbound transmission. Themethod further comprises the step of selecting the frequency reuse plan,based upon the subset.

Another aspect of the present invention is a controller in a two-wayradio messaging system for dynamically selecting a frequency reuse plan.The controller comprises a network interface for receiving a messagefrom a message originator, and a processing system coupled to thenetwork interface for processing the message. The controller furthercomprises an output interface coupled to the processing system forcommunicating with a plurality of base receivers. The processing systemis programmed to monitor, through the plurality of base receivers, aninbound channel for an inbound transmission from a portable subscriberunit. The processing system is further programmed to determine a subsetof the plurality of base receivers that reliably receive the inboundtransmission, and to select the frequency reuse plan, based upon thesubset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an electrical block diagram of a radio messaging system inaccordance with the present invention.

FIG. 2 is an electrical block diagram of portions of a base station andcontroller in accordance with the present invention.

FIG. 3 is an exemplary flow chart depicting operation of a firstembodiment of the radio messaging system in accordance with the presentinvention.

FIG. 4 is an exemplary flow chart depicting operation of a secondembodiment of the radio messaging system in accordance with the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, an electrical block diagram of a radio messagingsystem in accordance with the present invention comprises a fixedportion 102 including a controller 112 and a plurality of base stations116, and a portable portion including a plurality of portable subscriberunits 122, preferably having acknowledge-back capability. The basestations 116 are used for communicating with the portable subscriberunits 122 utilizing conventional radio frequency (RF) techniques, andare coupled by communication links 114 to the controller 112, whichcontrols the base stations 116.

The hardware of the controller 112 is preferably a combination of theWireless Messaging Gateway (WMG™) Administrator! paging terminal, andthe RF-Conductor!™ message distributor manufactured by Motorola, Inc.The hardware of the base stations 116 is preferably a combination of theNucleus® Orchestra! transmitter and RF-Audience!™ receivers manufacturedby Motorola, Inc. The portable subscriber units 122 are preferablyconventional Tenor™ voice messaging units and Pagefinder™ data messagingunits, also manufactured by Motorola, Inc. It will be appreciated thatother similar hardware can be utilized as well for the controller 112,the base stations 116, and the portable subscriber units 122.

Each of the base stations 116 transmits RF signals to the portablesubscriber units 122 via a transceiver antenna 118. The base stations116 each receive RF signals from the plurality of portable subscriberunits 122 via the transceiver antenna 118. The RF signals transmitted bythe base stations 116 to the portable subscriber units 122 (outboundmessages) comprise selective call addresses identifying the portablesubscriber units 122, and voice and data messages originated by acaller, as well as commands originated by the controller 112 foradjusting operating parameters of the radio communication system. The RFsignals transmitted by the portable subscriber units 122 to the basestations 116 (inbound messages) comprise responses that includescheduled messages, such as positive acknowledgments (ACKs) and negativeacknowledgments (NAKs), and unscheduled messages, such as registrationrequests. An embodiment of an acknowledge-back messaging system isdescribed in U.S. Pat. No. 4,875,038 issued Oct. 17, 1989 to Siwiak etal., which is hereby incorporated herein by reference.

The controller 112 preferably is coupled by telephone links 101 to apublic switched telephone network (PSTN) 110 for receiving selectivecall message originations therefrom. Selective call originationscomprising voice and data messages from the PSTN 110 can be generated,for example, from a conventional telephone 111 coupled to the PSTN 110.It will be appreciated that, alternatively, other types of communicationnetworks, e.g., packet switched networks and local area networks, can beutilized as well for transporting originated messages to the controller112.

The protocol utilized for outbound and inbound messages is preferablyselected from Motorola's well-known FLEX™ family of digital selectivecall signaling protocols. These protocols utilize well-known errordetection and error correction techniques and are therefore tolerant tobit errors occurring during transmission, provided that the bit errorsare not too numerous in any one code word. By using well-knowntechniques to count the number of errors detected in a predeterminednumber of code words, the controller 112 can easily determine the biterror rate of a received signal. It will be appreciated that othersuitable protocols can be used as well.

FIG. 2 is a simplified electrical block diagram of portions of the basestation 116 and controller 112 in accordance with the present invention.The controller 112 includes a processing system 210, a conventionaloutput interface 204, and a conventional network interface 218. The basestation 116 includes a base transmitter 206 and at least one basereceiver 207. At least a portion of the processing performed on voicemessages preferably is implemented in at least one conventional digitalsignal processor (DSP) 224 utilizing well-known techniques.

The processing system 210 is used for directing operations of thecontroller 112. The processing system 210 preferably is coupled throughthe output interface 204 to the base transmitter 206 via thecommunication link 114. The processing system 210 preferably also iscoupled through the output interface 204 to the base receiver 207 viathe communication link 114. The communication link 114 utilizes, forexample, conventional means such as a direct wire line (telephone) link,a data communication link, or any number of radio frequency links, suchas a radio frequency (RF) transceiver link, a microwave transceiverlink, or a satellite link, just to mention a few. In one embodiment thebase receiver 207 preferably includes a conventional received signalstrength indicator (RSSI) 230 for measuring the received signal strengthof an inbound transmission, utilizing well-known techniques. Theprocessing system 210 is also coupled to the network interface 218 foraccepting outbound voice and data messages originated by callerscommunicating via the PSTN 110 through the telephone links 101.

In order to perform the functions necessary for directing operations ofthe controller 112 and the base stations 116, the processing system 210preferably includes a conventional computer system 212, and aconventional mass storage medium 214. The conventional mass storagemedium 214 includes, for example, a subscriber database 220, comprisingsubscriber information such as addressing and programming options of theportable subscriber units 122.

The conventional computer system 212 is preferably programmed by way ofsoftware included in the conventional mass storage medium 214 forperforming the operations and features required in accordance with thepresent invention. The conventional computer system 212 preferablycomprises a plurality of processors such as VME Sparc™ processorsmanufactured by Sun Microsystems, Inc. These processors include memorysuch as dynamic random access memory (DRAM), which serves as a temporarymemory storage device for program execution, and scratch pad processingsuch as, for example, storing and queuing messages originated by callersusing the PSTN 110, processing acknowledgments received from theportable subscriber units 122, and protocol processing of messagesdestined for the portable subscriber units 122. The conventional massstorage medium 214 is preferably a conventional hard disk mass storagedevice.

It will be appreciated that other types of conventional computer systems212 can be utilized, and that additional computer systems 212, DSPs 224and mass storage media 214 of the same or alternative type can be addedas required to handle the processing requirements of the processingsystem 210. It will be further appreciated that additional basereceivers 207 either remote from or collocated with the base transmitter206 can be utilized to achieve a desired inbound sensitivity, and thatadditional, separate antennas 118 can be utilized for the basetransmitter 206 and the base receivers 207.

The mass medium 214 preferably includes software and various databasesutilized in accordance with the present invention. A message processingelement 222 is included for processing the voice and data messages. Inparticular, the mass medium 214 also includes an in-range receiversubset element 226 and a frequency plan selection element 228, whichprogram the processing system 210 to perform in accordance with thepresent invention, as is described further below. It will be appreciatedthat the controller 112 and the base station 116 can be eithercollocated or remote from one another, depending upon system size andarchitecture. It will be further appreciated that in large systems,functional elements of the controller 112 can be distributed among aplurality of networked controllers.

FIG. 3 is an exemplary flow chart 300 depicting operation of a firstembodiment of the radio messaging system in accordance with the presentinvention. The flow begins with the controller 112 and the basetransmitters 206 cooperating to send 302 a "where are you" (WRU) commandto one of the portable subscriber units 122. The controller 112 and thebase receivers 207 then monitor 304 the inbound channel for an inboundresponse from the portable subscriber unit 122. As the response isreceived by the base receivers 207, the controller 112 and basereceivers 207 cooperate to determine 306 a subset of the base receiversthat are reliably receiving the response. Reliable reception isdetermined as follows. In one embodiment, for example, the basereceivers 207 each measure the received signal strength with the RSSI230 and report the measured signal strength to the controller 112. Whenforming the subset of the base receivers 207 the controller 112 includesa base receiver 207 in the subset only when the received signal strengthmeasured for the base receiver 207 is greater than a predeterminedthreshold. In a second embodiment, for example, the processing system210 determines an error rate of each of the received signals, utilizingwell-known error detection techniques. Then, when forming the subset ofthe base receivers 207, the processing system 210 includes a basereceiver 207 in the subset only when the error rate measured for thebase receiver 207 is less than a predetermined threshold. It will beappreciated that, alternatively, other techniques, e.g., requiring asignal-to-noise ratio greater than a predetermined threshold, can beutilized to determine which base receivers should be included in thesubset as having "reliably received" the inbound transmission.

The controller 112 next determines 308 a count of how many basereceivers 207 are in the subset. The controller 112 accesses thefrequency plan selection element 228 to choose 310 a frequency reuseplan based upon the count. Preferably the frequency plan selectionelement 228 is preprogrammed with a selection of predetermined frequencyreuse plans cross referenced with the count such that co-channel spacingincreases as the count increases. The controller 112 then preferablyapplies 312 the chosen frequency reuse plan to a next outboundtransmission directed to the portable subscriber unit 122.Alternatively, the controller can apply the chosen frequency reuse planto a next inbound transmission from the portable subscriber unit 122instead of, or in addition to, applying the plan to the outboundtransmission. (The controller can direct the portable subscriber unit122 to use a specific inbound channel through well-known commandsincluded in the transmission protocol.)

FIG. 4 is an exemplary flow chart 400 depicting operation of a secondembodiment of the radio messaging system in accordance with the presentinvention. The first two steps of the flow chart 400 are identical tothe first two steps of the flow chart 300. At step 406 the controller112 determines a subset of the base receivers 207 that reliably receivethe inbound response AND are collocated with a base transmitter 206. Thecontroller 112 then selects 408 at least one base transmitter 206collocated with at least one base receiver 207 for sending a nextoutbound transmission to the portable subscriber unit 122. During theoutbound transmission, the controller 112 also inactivates for theduration of the outbound transmission all base transmitters other thanthe at least one base transmitter 206 that are collocated with a basereceiver included in the subset. By operating in this manner, thecontroller 112 advantageously dynamically forms and applies a frequencyreuse plan which prevents base transmitters that are within range of theportable subscriber unit 122 from interfering with the outboundtransmission.

Thus, it should be clear from the preceding disclosure that the presentinvention provides a method and apparatus in a radio messaging systemthat advantageously dynamically selects a frequency reuse plan for anoutbound and/or inbound communication with a portable subscriber unit.Desirably, the selected frequency reuse plan is determined from a subsetof transmitters measured to be within range of the portable subscriberunit.

Many modifications and variations of the present invention are possiblein light of the above teachings. Thus, it is to be understood that,within the scope of the appended claims, the invention may be practicedother than as described herein above.

What is claimed is:
 1. A method in a two-way radio messaging system fordynamically selecting a frequency reuse plan, comprising the stepsof:monitoring, by a plurality of base receivers, an inbound channel foran inbound transmission from a portable subscriber unit; determining acount of how many base receivers are in a subset of the plurality ofbase receivers that reliably receive the inbound transmission; andselecting the frequency reuse plan, based upon the count.
 2. The methodof claim 1, wherein the determining step comprises the step ofdetermining the subset of the plurality of base receivers that reliablyreceive the inbound transmission and are collocated with a basetransmitter.
 3. The method of claim 1, further comprising the step ofapplying the frequency reuse plan to at least one of an outboundtransmission and an inbound transmission.
 4. The method of claim 1,wherein the monitoring step comprises the step of monitoring the inboundchannel in response to having sent a command to the portable subscriberunit.
 5. The method of claim 1, wherein the determining step comprisesthe steps of:measuring by the plurality of base receivers a receivedsignal strength of the inbound transmission; and including a basereceiver in the subset only when the received signal strength measuredfor the base receiver is greater than a predetermined threshold.
 6. Themethod of claim 1, wherein the determining step comprises the stepsof:measuring by the plurality of base receivers an error rate generatedby the inbound transmission; and including a base receiver in the subsetonly when the error rate measured for the base receiver is less than apredetermined threshold.
 7. The method of claim 1, wherein the selectingstep comprises the step of selecting at least one base transmittercollocated with at least one base receiver of the subset for sending anoutbound transmission.
 8. The method of claim 7, wherein the selectingstep further comprises the step of inactivating all base transmitterscollocated with a base receiver of the subset other than the at leastone base transmitter during the outbound transmission.
 9. The method ofclaim 1, wherein the selecting step comprises the step of selecting thefrequency reuse plan such that co-channel transmitter spacing increasesas the count increases.
 10. A controller in a two-way radio messagingsystem for dynamically selecting a frequency reuse plan, the controllercomprising:a network interface for receiving a message from a messageoriginator; a processing system coupled to the network interface forprocessing the message; and an output interface coupled to theprocessing system for communicating with a plurality of base receivers,wherein the processing system is programmed to: monitor, through theplurality of base receivers, an inbound channel for an inboundtransmission from a portable subscriber unit; determine a count of howmany base receivers are in a subset of the plurality of base receiversthat reliably receive the inbound transmission; and select the frequencyreuse plan, based upon the count.
 11. The controller of claim 10,wherein the processing system is further programmed to determine thesubset of the plurality of base receivers that reliably receive theinbound transmission and are collocated with a base transmitter.
 12. Thecontroller of claim 10, wherein the processing system is furtherprogrammed to apply the frequency reuse plan to at least one of anoutbound transmission and an inbound transmission.
 13. The controller ofclaim 10, wherein the processing system is further programmed to monitorthe inbound channel in response to having sent a command to the portablesubscriber unit.
 14. The controller of claim 10, wherein the processingsystem is further programmed to:measure through the plurality of basereceivers a received signal strength of the inbound transmission; andinclude a base receiver in the subset only when the received signalstrength measured for the base receiver is greater than a predeterminedthreshold.
 15. The controller of claim 10, wherein the processing systemis further programmed to:measure through the plurality of base receiversan error rate generated by the inbound transmission; and include a basereceiver in the subset only when the error rate measured for the basereceiver is less than a predetermined threshold.
 16. The controller ofclaim 10, wherein the processing system is further programmed to selectat least one base transmitter collocated with at least one base receiverof the subset for sending an outbound transmission.
 17. The controllerof claim 16, wherein the processing system is further programmed toinactivate all base transmitters collocated with a base receiver of thesubset other than the at least one base transmitter during the outboundtransmission.
 18. The controller of claim 10, wherein the processingsystem is further programmed to select the frequency reuse plan suchthat co-channel transmitter spacing increases as the count increases.